This invention pertains generally to a contact assembly for an electrical circuit breaker which has a contact lever and a lever support flexibly connected to the contact lever, and more particularly to a lever support which can be swivelled around a fixed bearing by a drive mechanism for on- and off-switching. Such a contact arrangement has a contact spring positioned between the contact lever and the lever support and a circuit-generated current-dependent force can be conveyed to the contact lever to increase the contact force.
A contact assembly of the type described above is disclosed in U.S. Pat. No. 2,704,311. Similar contact assemblies are disclosed in U.S. Pat. Nos. 3,550,049 and 2,695,345 and in German Pats. Nos. 11 16 782 and 12 18 594. In these patents, the current-dependent forces impact one arm of the contact levers which is positioned facing the arm equipped with the movable contact piece. The assembly is based on the fact that the direction of the current-dependent forces is determined by the loop-shaped design of the current circuit. For that purpose, a flexible conductor is frequently utilized, because it is already required to connect a fixed-mounted conductor bus bar to the movable components of the contact assembly. The current-dependent forces are required so that even if large fault currents flow, adequate contact force is ensured until the tripping devices of the circuit breaker provides a switch-off signal.
When switching on these types of contact assemblies, the contact lever is initially shifted into a position largely parallel to itself using its associated lever support until the movable contact piece makes contact with the associated fixed contact piece. The lever support, however, also performs a further motion during which the contact spring is tensioned. This process is linked with a swivelling motion of the contact lever around its fulcrum at the lever support. Is has been observed that during the switch-on cycle the contact lever can bounce around its pivot bearing at the lever support caused by the impact of the contact pieces. This chattering effect is undesirable since it can lead to damage and fusion of the contact pieces. Accordingly, it will be appreciated that it would be highly desirable to provide a contact assembly of the type specified above so that this chatter effect is eliminated during the switch-on cycle.
Existing contact assemblies for low-voltage circuit breakers already incorporate special pressure levers to increase the contact force. These pressure levers are equipped with an armature of a magnetic system excited by the current flowing through the contact assembly. The corresponding yoke of the magnetic system is located at the lever support of the contact assembly. While this assembly does lead to a relatively favorable bouncing action, it is relatively expensive to construct, and, in terms of its attainable compensation force to the current loops, it is not suitable for circuit breakers which are to attain a breaking capacity of approximately 100 kA. See Technical Publication, "Power Engineering II," 8th edition, 1960, pages 53 and 85 of an offprint of the chapter on "Low-Voltage Switchgear."
It is an object of the present invention to provide a contact assembly for a circuit breaker which reduces contact bounce.
Another object of the invention is to provide a contact assembly which prevents fusion of the contact pieces.